This invention relates to the art of portable motor-driven tools, and more particularly to a new and improved safety measure for such tools.
One area of use of the present invention is in portable motor-driven tools where the work output is provided by a rotating shaft, although the principles of the present invention can be variously applied. In the operation of portable motor-driven tools, for example drills, automatic screwdrivers, tappers, tube expanders and the like, it sometimes happens that during use the tool, such as a drill bit, becomes stuck or lodged in the workpiece. If this happens, the entire motor reaction force then is transferred to the housing which normally is held in the operator's hand. If the tool becomes stuck in the workpiece suddenly, the resultant sudden reverse torque may be sufficiently great to cause the operator to lose his grip on the tool and even to be forced off balance himself. The foregoing presents safety hazards and possibility of serious personal injury and also costly damage to equipment.